I found this thread -v useful:

http://forums.moneysavingexpert.com/...=138388&page=6

basically they change the code periodically - I believe daily. Code can only be used for single trips (not return). But if 2 of you travelling together use the code to add one single, then go back and add another single to your cart before checking out. I did this the other day for upciming travel - I think we will have to use different cards in the machine to pick up (not necessarily the card used to purchase).

The above also allows one to use 50 WorldPoints to get multiple 50% off discounts - and once you have the code you can re-use it, or anyone else can. So if someone gets a code could they post it here - thanks.